Self-assembling molecules that form self-assembled films, typically, monolayer films, have been used in a variety of applications. For example, they have been used for modifying the properties of metal surfaces, forming small dimension patterns on solid substrates, producing sensors for biological molecules, and reducing friction and modifying the surface energy of the orifices of ink jet pens. They have also been used to provide a protective barrier against water and corrosive substances that typically attack metal surfaces, and to promote adhesion of overlying polymers to metal surfaces.
Self-assembled thin films are most often prepared by dip coating a substrate of interest in a dilute solution of the self-assembling amphiphile or by exposure to a vapor phase containing the amphiphile, and allowing film formation to proceed. The molecules spontaneously create a generally organized molecular architecture on the substrate. Once formed, the film does not redissolve in the solvent from which it was deposited, unlike polymer films that are not self-assembled. The long dwell times and flammable solvents often used make this processing user-unfriendly and difficult to adapt to a manufacturing setting. Thus, new means of providing self-assembled films are desired.
The compositions of this invention provide a means to eliminate costly or inconvenient steps in the generation of modified surfaces by incorporating a precursor to a self-assembling monolayer film into an adhesive composition. The self-assembling molecules are chosen such that they have an affinity for the substrate to be modified, a controlled solubility in the adhesive, and a molecular architecture such that when the self-assembling precursor finds the substrate surface, it attaches and spontaneously forms a film at the interface between the adhesive and the substrate.
Thus, the present invention provides adhesive compositions that include self-assembling molecules, adhesives and adhesive articles produced therefrom, and methods of making and using such adhesives. These materials are advantageous because the adhesive composition can serve a variety of functions. For example, the adhesive composition of the present invention can serve as a delivery vehicle for self-assembled films, such as low-surface-energy films, that can function as release agents for the adhesive component. A low-surface-energy film can then protect a surface, such as a metal oxide or other inorganic surfaces. The adhesive composition of the present invention can also be used as a self-priming adhesive, such that a surface to which an adhesive does not adhere well, e.g., an oily or otherwise contaminated surface, particularly a metal surface, does not need to be separately primed.
In one embodiment there is provided an adhesive composition that includes an adhesive component and a precursor of an in-situ self-assembled film capable of modifying a property of a surface to which the adhesive is applied. A method of modifying a property of a surface is also provided. The method includes applying to the surface an adhesive composition that includes an adhesive component and a precursor of an in-situ self-assembled film capable of modifying a property of the surface to which the adhesive composition is applied. Herein, a xe2x80x9cprecursor of an in-situ self-assembled filmxe2x80x9d is also referred to as xe2x80x9cprecursorxe2x80x9d or xe2x80x9cself-assembled film precursorxe2x80x9d or xe2x80x9cself-assembling moleculesxe2x80x9d and has the structure Yxe2x80x94Zxe2x80x94(CQ2)nxe2x80x94Wxe2x80x94X wherein: Y is H, a halogen, a functional group capable of interacting with the adhesive, or an organic group optionally including a functional group capable of interacting with the adhesive (preferably, for certain embodiments the organic group is a perfluoroalkyl group); Z is a covalent bond or an organic linking group; Q is H or F; W is a covalent bond or an organic linking group; X is a nonionic group that interacts with a substrate on which the adhesive composition is disposed; and n is at least about 7; with the proviso that (CQ2)n does not include CHF groups or alternating CH2CF2 groups; wherein the compound is substantially insoluble in neutral water characterized in that a mixture of greater than 0.1% by weight of the compound in neutral (pH about 7) water results in a multiphase composition. Herein, an interaction between any two materials (e.g., adhesive and functional group within self-assembled film or substrate and functional group within self-assembled film) can be attractive, repulsive, or a bonding interaction (e.g., covalent or ionic).
In another embodiment there is provided an adhesive bonded to a substrate. The adhesive includes an adhesive component and a self-assembled thin film prepared from a precursor having the structure described immediately above. Herein, a film refers to mono- or multimolecular layers, each layer being on the order of about 5 Angstroms to about 30 Angstroms thick, with the entire film being less than 500 Angstroms thick. The most preferred layer thickness is monomolecular.
Yet another embodiment of the invention includes articles with at least two substrates bonded together with the adhesives disclosed herein. Preferably, the substrates are metal substrates or metal oxide substrates. Preferably, the substrates are bonded together by an adhesive bond that retains its strength after exposure to elevated temperature (e.g., up to about 71xc2x0 C.), elevated humidity (e.g., up to about 100%), salt water (e.g., at a concentration of about 2 wt % to about 6 wt %), or combinations thereof.
Another embodiment is directed to an adhesive composition that can provide a low-surface-energy film and a method of providing a low-surface-energy film on a surface. The adhesive composition includes an adhesive component and a precursor of an in-situ self-assembled low-surface-energy film having a surface energy less than about 35 dynes per centimeter (dynes/cm). The method includes applying to the surface such an adhesive composition. Preferably, the method further includes removing the adhesive component. In these low-surface-energy embodiments, preferably the precursor is of the structure Yxe2x80x94Zxe2x80x94(CQ2)nxe2x80x94Wxe2x80x94X wherein: Y is H, F, or a perfluoroalkyl group of the formula CmF2m+1 where m is no greater than about 10; Z is a covalent bond; Q is H or F; W is a covalent bond or an organic linking group; X is a nonionic group that interacts with a substrate on which the adhesive composition is disposed; and n is at least about 7; with the proviso that (CQ2)n does not include CHF groups or alternating CH2CF2 groups; and wherein at least about 0.1% by weight of the precursor in neutral water at 22xc2x0 C. forms a multiphase composition.
Another embodiment is directed to an adhesive composition that is self-priming and a method of eliminating the need for priming a surface. The self-priming adhesive composition includes an adhesive component and a precursor of an in-situ self-assembled film. The method includes applying to the surface such a self-priming adhesive composition. In these self-priming embodiments, the precursor is of the structure Yxe2x80x94Zxe2x80x94(CQ2)nxe2x80x94Wxe2x80x94X wherein: Y is a functional group capable of interacting with the adhesive component, or an organic group optionally including a functional group capable of interacting with the adhesive component; Z is a covalent bond or an organic linking group; Q is H; W is a covalent bond or an organic linking group; X is a nonionic group that interacts with a substrate on which the adhesive composition is disposed; and n is at least about 7; and wherein at least about 0.1% by weight of the precursor in neutral water at 22xc2x0 C. forms a multiphase composition.
Methods of making adhesive compositions are also provided. Such methods vary depending on the type of adhesive component used. As used herein, xe2x80x9caxe2x80x9d or xe2x80x9canxe2x80x9d or xe2x80x9cthexe2x80x9d are used interchangeably with xe2x80x9cat least one,xe2x80x9d which mean xe2x80x9cone or morexe2x80x9d of the element being modified.